The present invention relates to cementing compositions and slurries that are useful for water control in oil and gas wells. In particular, the invention relates to such compositions for use in squeeze cementing operations.
One of the principal reasons of the abandonment of producing gas or oil wells is the increased production of water which renders continued exploitation of the well unprofitable. This water can come from the underground formation constituting the gas or oil reservoir. There are many different cases that can arise. Amongst the most frequent are the following. The rise of the water level can result from the simple progressive depletion of the producing oil and/or gas layer(s). This is a general rise of level of water in the formation. If the well is cased, the water level eventually reaches the level of perforations in the casing adjacent the gas or oil producing zone(s). If the well is completed without lining (barefoot), the general rise of the level of water leads a greater part of the well being open to water and the proportion of water in the aggregate output increases. A rise in the level of water can occur locally, around the producing zones. This is due to the difference in pressure between the pressure of the fluids in the formation and the pressure maintained in the well to obtain the production (called xe2x80x9cwater coningxe2x80x9d). This local rise can be also supported by fractures with strong dip.
The increase in water can also result from water injection by the operator. This water injection, sometimes called xe2x80x9cwater floodxe2x80x9d, is achieved by the use of water injection wells and the objective is to maximize the oil recovery. The sweeping of the formation by the water flood is almost always irregular and the water produced by the wells of production increases, either as a result of preferentially producing formation water or producing the injection water itself. Lastly, when there is damage to cement used together with casing for zonal isolation, water can come from a geological layer different from the desired producing layer.
In such cases, the current technique for remediation consists plugging specific zones with organic or mineral gel or cement grouts. The cement used can be a construction cement, an oilfield cement or a microcement useful for penetrating narrower fractures. These various techniques present advantages and disadvantages. According to the case, these can be used separately or together. However, all these techniques present the same disadvantage: they are not selective. The use of these cements or gels can result in plugging the water flow, which is desirable, or plugging the gas or crude oil flow, which is undesirable. Consequently, it is desirable to place these fluids in a precise way. This requires a very good identification of the phenomenon leading to the production of water but this is not always possible because of the depth of the wells and the frequent presence of metal casing, which masks the phenomena. Cement placement is therefore always very difficult and hazardous owing to the fact that there is no certainty in the position of the water flow to be stopped.
For this reason, it has been sought to develop formulations containing cement which would only remain where water is actually produced. This is the object of the two U.S. Pat. No. 5,238,064 (1993) and U.S. Pat. No. 5,348,584 (1994). In these two patents, the inventor proposes to disperse cement or microcement in a hydrocarbon phase. Surfactants are added before or during dispersion. These processes are industrial. In spite of their theoretical advantage, they are rarely used, because the rate of success is only very moderate. Bringing the particles suspended in a hydrocarbon into contact with water is difficult. The presence of hydrocarbons in the suspension is source of pollution and thus undesirable in many parts of the world.
The present invention relates to cementing compositions and slurries that are useful for water control in oil and gas wells.
The present invention comprises dispersing a hydraulic cement powder in a solvent that is miscible both with water and hydrocarbons to make a slurry. The cement powder can be made up simply of hydraulic cement materials or can be a mixture of such materials with particles that are inert or reactive with cement as disclosed in EP 0 621 247, EP 0 748 782, WO 00 34199 or EP 0 922 013.
The various cement materials can be of any nature, Portland cement, optionally including pozzolans such as for example blast furnace slags or fly ash or cenospheres, or natural materials such as pozzolan or calcined clays. One can also use aluminate cements (Fondu Lafarge), plaster, Sorel cement, pozzolanic activated cements or all other composition with hydraulic set properties (hereinafter simply called xe2x80x9ccementxe2x80x9d). The maximum size of the cement particles is of no importance on the level of selectivity, it can therefore be selected according to the size of fractures to be plugged. One can use, as an example ordinary cement, of which more than 90% of the particles have a size lower than 100 microns, or well microcement, of which more than 90% of the particles have a size lower than 10 microns or less, or cements of intermediate size, or mixtures of the preceding.
When using formulations including, in addition to the cement particles previously defined, the different particles according to the disclosure of EP 0 621 247, EP 0 748 782, WO 00 34199 or EP 0 922 013, care should be taken that the added sub-micron particles are not in suspension in water. Particles of sizes lower than one micron have a tendency to agglomerate in a dry state because of the interparticulate forces of attraction. It can then become very difficult or impossible to re-disperse them. For this reason, they are presented usually in the form of suspension in a liquid. Such fine particles are used as suspended in oil or a solvent miscible with the solvent being used to manufacture the slurry. Such suspensions of mineral particles exist on the market as pigments for paints.
The solvent miscible with water and hydrocarbons used to make the slurry can belong to many families of temperature stable products, such as ethers and polyethers (e.g. tetrahydrofurane, dioxane, ethylene glycol monoalkyl ethers or poly-ethylene-glycol monoalkyl ethers), or anhydrous alcohols of low molecular mass (e.g. methanol, ethanol or propanols), ether-alcohols e.g. 2-butoxyethanol, amides (e.g. N, N-dimethyl- or N, N-diethylformamide, N, N-dimethyl- or N, N-diethylacetamide or N-methylacetamide). Generally, the solvent will be selected from products considered as miscible with water or very soluble in benzene in the tables of physical constants such as those published in reference works such as the xe2x80x9cCRC Handbook of Chemistry and Physicsxe2x80x9d. Either pure solvents or mixtures of the solvents can be used. In particular, slightly volatile solvents having a good temperature stability and strict environmental acceptability are preferred.
Surfactant solids can be added to disperse the solid particles. According to solvent selected, polynaphtalenesulfonates, polymelaminesulfonates, substituted succinimides or substituted sulfosuccinimides can be used. These products will typically not be used in aqueous solution, but either in the solid state or prediluted in one of the anhydrous solvents proposed above. Normally, it will not be necessary to add retarder to the cement as there is no water in the slurry to set the cement during placement and as a rapid set is desired after placement where the slurry is in contact with water. However if it is desired to add a retarder for specific water control intervention, lignosulfonate, glucoheptonic acid or salts, or derivatives of glyceroheptonates, a mixture of lignosulfonate with a gluconate, diphenols such as cathechol, hydroquinone, or resorcinol can be used. All these retarders are well-known in this field.
The slurry typically contains from 20% to 65% by volume of solid products. When the formulation contains cement of normal particle size (without using the teaching of EP 0 621 247), the slurry typically contains from 20 to 50% of solid. When using cement of normal particle size, but by applying the teaching of EP 0 621 247, the range is extended to 65% by volume of solid. When the formulation uses microcements the range is typically 15 to 47% by volume of solid in suspension. While formulating with microcement according to WO 00 34199, i.e. by adding submicron particles, the quantity of solid in suspension can be extended to 55% by volume of solid.
The slurry is used in the manner of a squeeze cement (forced injection of slurry) in the well. Where it meets water, the slurry sets and plugs the cracks, slits or porosity from which the water is produced. There is no special problem for wetting of the particles, particularly those of cement, because of the compatibility of solvent used with water. Where the slurry meets oil or condensates of oil, there is no set, because due to the compatibility of solvent with oil or the condensates, the slurry is diluted and ejected. The cracks, slits and pores, from which the crude oil is produced before the intervention, remain exposed and oil or the condensates can still flow therethrough.